BERNARD L. STREHLER 219 



same reactions are occurring under both conditions. Although it seems 

 probable that flavin in association with luciferase and perhaps long- 

 chain aldehyde, is the light-emitting complex, the considerable dif- 

 ference between the emission maxima exhibited by riboflavin fluores- 

 cence and chemiluminescence on the one hand, and the emission of 

 the bacterial extracts on tlie other, is a puzzling and possibly crucial 

 point at issue. 



At least four solutions to this diflRculty may. be suggested. The first 

 is simply that the flavin is not the emitting molecule, even though the 

 biochemical evidence is fairly convincing that flavin is directly con- 

 nected with light emission. The second possibility is that the broad 

 flavin fluorescent and chemiluminescent emission is made up of tran- 

 sitions from two different excited states and that only the more ener- 

 getic of these is formed during the enzymatically catalyzed chemi- 

 luminescence. The third alternative is that the binding of the flavin 

 to the enzyme hinders the occurrence of certain vibrational modes, 

 thus largely preventing transitions from the excited state, to higher 

 vibrational levels of the ground state and consequentl}' shifting the 

 emission closer to the absorption band. The final possible solution to 

 the difficulty is that the emission in the longer region of the spectrum 

 is quenched by a pigment in the bacteria. Sir.ce there is no evidence 

 that such compounds occur in appreciable amounts in luminous bac- 

 teria, the process would of necessity involve a mechanism analogous 

 to sensitized fluorescence, with the condition that there is a \ery low 

 yield of fluorescence from the absorbing entity. 



Nature of Enzyme — General Properties 



The enzyme will not pass through a dialysis membrane, is destroyed 

 by heat, and is nonparticulate (as evidenced by its lack of precipita- 

 tion under ultracentrifugation ) . It is sensitive to dilution, inhibited by 

 sulfhydryl inhibitors (Hg++ and p-chloromercuribenzoate), and can 

 be frozen and thawed repeatedly without destroying its activity'. It 

 can be separated from some impurities by precipitation with acid, 

 acetone, and (NH4)oS04. Dr. Green in Dr. McElroy's laboratory is 

 presently engaged in preparing this enzyme in purified form. Whether 

 or not the various activities exhibited by this enzymatic extract in the 

 luminescent sequence of reactions are due to a single component or 



